Quantitative analysis of chimerism after allogeneic peripheral blood stem cell transplantation

For peripheral blood stem cell transplantation (PSCT), several engraftment analysis methods have been performed including detection of restriction fragment length polymorphisms and amplification of polymorphic genetic loci. To facilitate monitoring of the engraftment, a quantitative, non-isotopic method using a short tandem repeat (STR) marker has been set up in our laboratory.

DNAs from pretransplant recipients and donors were amplified with the AmpFISTR Profiler Plus kit that contains 9 STR markers. The fluorescent polymerase chain reaction products were then fractionated on polyacrylamide gels in an ABI PRISM 377 DNA sequencer. Results were analyzed using GeneScan 2.1 software. We selected the best markers as informative alleles which can distinguish donor from recipient. For quantitative analysis of the engraftment, we prepared a mixed chimeric sample by mixing pretransplant recipient and donor DNAs in different ratios to produce a standard curve. After amplifying the posttransplant recipient DNA, we were able to detect the extent of engraftment by interpolating the percent peak area of the informative alleles from this standard curve.

We retrospectively analyzed 10 patients who had received allogeneic PSCT. Two of them showed some degree of mixed chimerism indicating leukemic relapse. In case one, 38.7% of the recipient DNA was first detected in the third month after PSCT. In case two, 6.5% of the recipient DNA was first detected in the tenth month after PSCT.

In summary, this method provides an accurate, quantitative, and early assessment of mixed chimerism in posttransplant patients. Such information may be useful to guide implementation of additional treatment to circumvent graft failure or relapse in the future.